1. Field of the Invention
The present invention generally relates to a fuel injection control system for an internal combustion engine and, more particularly, to a fuel injection control system which controls a timing for injecting fuel to each of a plurality of engine cylinders.
2. Description of the Related Art
Conventionally, as disclosed in Japanese Patent Publication No.2-45018, a fuel injection control system for an internal combustion engine, which controls the timing for injecting fuel to each of a plurality of engine cylinders, is known. In this system, when a starter switch of the engine is turned on, fuel is injected first to each of the engine cylinders without considering a synchronization with an engine crank angle. Hereinafter, this fuel injecting operation is referred to as an asynchronous injection. In the above-mentioned apparatus, after the starter switch is turned on and the first suction stroke is completed in each of the cylinders, fuel is sequentially injected to each of the cylinders in a predetermined order in synchronization with the crank angle. Hereinafter, this fuel injecting operation is referred to as synchronous injection.
According to the above-mentioned conventional fuel injection control system, fuel is rapidly supplied to a plurality of engine cylinders during a starting operation of the internal combustion engine. Additionally, since the synchronous injection is not started until an intake stroke is completed in each of the cylinders, the fuel supplied by asynchronous injection is prevented from being mixed with the fuel supplied by the synchronous injection. Thus, an air-fuel mixture is prevented from being over-rich.
However, in an internal combustion engine, in order to supply an ignition signal to each of a plurality of engine cylinders at an appropriate time, a condition of each of the cylinders must be accurately determined. The condition of each of the cylinders cannot be detected until a predetermined change has been generated in an angle of a crank shaft after the internal combustion engine is started. Accordingly, the ignition signal cannot be supplied to each of the cylinders until the predetermined change is generated in the crank angle after the internal combustion engine has been started.
As mentioned above, the conventional fuel injection control system performs asynchronous injection for each of the engine cylinders after the starter switch is turned on. After the starting operation of the internal combustion engine is initiated and before the predetermined change is generated in the crank angle, the fuel supplied by asynchronous injection is exhausted without being ignited. In this respect, the above-mentioned conventional fuel injection control system could possibly deteriorate exhaust emissions during a starting operation.